A radiation therapy or diagnostic imaging device generally includes a gantry which can be swiveled around a horizontal axis of rotation in the course of a therapeutic treatment or diagnostic imaging. A patient is supported in a substantially rigid position on a tabletop while the patient is exposed to a radiation source or imaging is performed. In radiation therapy, an electron linear accelerator is located within the gantry for generating a high energy radiation beam for therapy. This high energy radiation beam may be an electron beam or photon (x-ray) beam, for example. During treatment, the radiation beam is trained on a zone of a patient lying in an isocenter of the gantry rotation. The radiation source is typically movable about the table so that the patient can be exposed to radiation from all possible angles so that radiation can be directed at the tumor site to destroy a tumor and minimize exposure to healthy tissue.
Linear accelerators may be used in the medical environment for a variety of applications. A beam of charged particles (e.g., electrons) from a linear accelerator may be directed at a target which is made of a material having a high atomic number, so that an x-ray beam is produced for radiation therapy. Alternatively, the beam of charged particles may be applied directly to a patient during a radiosurgical procedure. Such radiosurgery has become a well-established therapy in the treatment of brain tumors. A high-energy beam may be directed at a localized region to cause a breakdown of one or both strands of the DNA molecule inside cancer cells, with the goal of at least retarding further growth and preferably providing curative cancer treatment.
For radiation therapy, diagnostic imaging, surgery, and other medical procedures, a patient is placed on a tabletop supported by a table structure. The tabletop is typically a cantilever structure configured to position the patient in the beam area with room on the exit side for imaging equipment. For certain radiation therapy programs, a patient treatment area is immobilized for accurate radiation delivery during the course of treatment. The tabletop is used to maintain the patient in a rigid, properly aligned position to prevent harm to healthy body tissue. In treatments where immobilization is planned, this is typically done by means of a thermoplastic sheet which is custom formed over the patient and attached to an anchoring panel. In some applications, the anchoring panel rests on the tabletop with no direct physical attachment. In other applications, the anchoring panel clamps to the tabletop or attaches to plates which clamp in set positions. These techniques require the therapist to accurately reproduce a variable setup.
For typical programs, a patient may have imaging or scanning performed on one type of tabletop, simulation on another tabletop, and treatment delivered utilizing another tabletop. It is generally desired that the same tabletop construction is used throughout the treatment program so that the setup of the patient is consistent throughout the treatment.
For radiation therapy, imaging, simulation, and delivery, it is desirable for the patient support tabletop surface to be generally planar and rigid to provide accuracy and repeatability. It is also desirable for a tabletop surface to have a minimum effect on radiation transmission in order to maintain high imaging and beam quality, as well as minimize loss of deliverable dose and skin sparing for treatments that are directed through the tabletop structure before reaching the patient.
High rigidity has typically been achieved by panels with a thickness of one cm or greater. One drawback to these structures is that they typically do not have acceptable transmission or skin sparing properties required for certain types of treatments. High transmission factors have typically been achieved by a mesh grid work or “racquet”, constructed with a woven pattern. However, these tabletop designs often do not provide an acceptable rigidity to provide consistent positioning and patient support. In order to overcome strength and rigidity problems, conventional tabletops typically include metal components within the tabletop structure to increase strength and rigidity or provide fastener support for tabletop attachments. The metal components often interfere with the treatment or diagnostics since they impact transmission and appear as artifacts in imaging. The metal tabletop structure may also block some of the radiation rays or attenuate the radiation, resulting in inaccurate dosing. This may occur even if the material of the tabletop is not metal but has significant thickness, such as with a composite sandwich design.
There is, therefore, a need for a tabletop system that provides acceptable strength and rigidity without interfering with the treatment or imaging performed on the patient.
Furthermore, conventional patient positioning devices include immobilization devices that are positioned on top of the surface of the tabletop and require locking to the surface or alignment to lateral and independent positioning lasers, as well as, placement and replacement of the accessory immobilization devices to the surface of the diagnostic and treatment tabletops. These immobilization devices are often heavy and difficult to position on the tabletop. It is therefore, desirable to have immobilization devices that are integrated into the tabletop design, thus reducing the need for repeated positioning of the devices on the tabletop.